Remove 50GB oldest files in busybox when used capacity reaches 95%

Question

Ok I have requested a code here but initial I didn't ask to make it busybox compatible. My bad. I'm new to Linux and coding.

The code needs to do the following:

Delete 50GB of oldest data (dir with files) from a directory when the HD reaches a capacity of 95%.

The code they gave me is, that is not working with busybox:

DIRS="a/ b/"
MAXDELBYTES="53687091200" # 50GB
DELBYTES="0"

find $DIRS -type f -printf "%T@ %s %p\n" | sort -r -n | while read time bytes filename
do
    rm -fv "$filename"
    DELBYTES=$((DELBYTES + bytes))

    if [ $DELBYTES -ge $MAXDELBYTES ]; then break; fi
done

What is not working:

• -printf (changed it to -print)
• %T@ %s %p\n (don't know what to change it to)
• Do not know what else isn't working. I'm new to coding and Linux.

Now this need to be translated to busybox so it will work on my embedded Linux system. Also a cron command needs to be added so it runs every Friday.

Answer 1

Since the busybox implementation of find does not offer custom output formatting, you need to outsource the formatting task to a separate program :) Luckily, even busybox includes the handy stat command. It's output format fields differ from the ones that GNU find uses, so the symbols you need to use are different. The script below assumes that find and stat are those that come from busybox.

DIRS="a/ b/"
MAXDELBYTES="53687091200" # 50GB
DELBYTES="0"

find $DIRS -type f -exec stat -c "%Y %s %n" {} \; | sort -r -n | while read time bytes filename
do
    rm -fv "$filename"
    DELBYTES=$((DELBYTES + bytes))

    if [ $DELBYTES -ge $MAXDELBYTES ]; then break; fi
done

As always, read each command's description before you use it. In case of busybox, you won't find manpages for them, but you can use --help to display usage information.

Be warned, that this solution can break things in an unlikely situation, when file names contain newline symbols in them! This should not occur on a healthy system, but might happen, for instance, if someone manages to either break into the system or exploit some vulnerability that allows arbitrary file creation.

To prevent accidentally removing useful files in such cases, you should first find and remove all files that include newlines in their names. To list those, run:

find / -name "*
*"

(There is only a newline between the asterisks.) Then, when you're sure all those files are not needed, delete them using either

find / -name "*
*" -delete

or

find / -name "*
*" -print0 | xargs -0 rm -vf

Both should work with busybox.

Answer 2

Generally, it's a bad idea to parse the output of ls. But on an embedded system that has no stat, no zsh, no find -printf, no perl or other large scripting language, it's the only way of sorting files by date. Assuming that your file names contain no whitespace and none of \'" (which xargs mangles) — an assumption that your original script makes — you can use xargs ls -str to display files sorted by date, and display their size in the process.

find $DIRS -type f |
xargs ls -str |
while read kilobytes filename; do …

Note that the size is displayed in kilobytes instead of bytes. Furthermore, this is the on-disk space taken by the file rather than the number of bytes in the file. Usually, this number is the file size, rounded up to the next integer number of blocks, but it may be less if the file is sparse. In a script that frees disk space, this is probably what you want.

There is a big caveat with the script above: it will only print its results in the right order if the number of files is small enough that xargs can make a single call to ls. If there are multiple calls to ls, each call will sort its arguments separately. You can print the file dates with ls, but sorting this human-readable output is very complicated. A better solution to at least detect the error case is to substitute the output of find into the command line.

{ set -f; IFS='
'; ls -str $(find $DIRS -type f); } |
while read -r kilobytes filename; do …